Federal authorities say they've arrested a Detroit man who bought explosives from an undercover agent after amassing weapons and talking about carrying out an attack.
A criminal complaint filed Monday charges 29-year-old Sebastian Gregerson with unregistered possession of a destructive device and unlicensed receipt of explosive materials.
The complaint chronicles a counterterrorism investigation that began in April 2015 following a tip about Gregerson, who the FBI says also is known as Abdurrahman bin Mikaayl. The investigation found that Gregerson bought a big arsenal of weapons, ammunition, tactical gear and training materials including hundreds of rounds of AK-47 ammunition, road spikes and two ski masks.
The FBI says he bought grenades on Sunday from the undercover agent outside a gas station in Monroe.
Authorities say Gregerson arrived at the meeting with a Beretta M9 that he said he would use as payment for the grenades.
After the exchange was made, Gregerson was taken into custody.
He's being held pending a Thursday detention hearing in U.S. District Court.